Re implement message field links #195
Description
Under the old documentation, the types had links, so that one could navigate to a field's type, directly from the message, now it doesn't.
For example: Going from https://docs.ros.org/en/ros2_packages/jazzy/api/sensor_msgs/msg/Imu.html to https://docs.ros.org/en/ros2_packages/jazzy/api/std_msgs/msg/Header.html is complex.
But going from http://docs.ros.org/en/noetic/api/sensor_msgs/html/msg/Imu.html to http://docs.ros.org/en/noetic/api/std_msgs/html/msg/Header.html is just a single click.